alkynes c n h 2n-2 dr. marwa eid 1. alkyne alkynes contain a triple bond. general formula is c n h...
TRANSCRIPT
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AlkyneAlkynes contain a triple bond.General formula is CnH2n-2
Two elements of un-saturation for each triple bond.
Some reactions are like alkenes: addition and oxidation.
Some reactions are specific to alkynes.
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NomenclatureFind the longest chain containing the triple
bond.Change -ane ending to -yne.Number the chain, starting at the end closest
to the triple bond.Give branches or other substituent a number
to locate their position.
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CH3 CH
CH3
CH2 C C CH
CH3
CH3
CH3 C C CH2 CH2 Br
CH3 C CH
propyne
5-bromo-2-pentyne
2,6-dimethyl-3-heptyne
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AcetyleneAcetylene, the simplest alkyne
Acetylene is used in welding torches.
(In pure oxygen, temperature of flame reaches 2800C)
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Synthesis of AcetyleneHeat coke with lime in an electric furnace to
form calcium carbide.Then drip water on the calcium carbide:
coke limeC CaO3 + +CaC2 CO
H C C H Ca(OH)2CaC2 + 2 H2O +
Calcium carbide
Electric furnace
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Synthesis of AcetyleneAcetylene is produced industrially from
methane and steam at high temperature
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HydrogenationAddition of Hydrogen in the presence of
metal catalyst (Pd, Pt, or Ni) to reduce alkyne to alkane, completely saturated.
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HydrogenationAddition of Hydrogen in the presence of
metal catalyst (Pd, Pt, or Ni) to reduce alkyne to alkane, completely saturated.
You can use a reduced activity catalyst (Lindlar), Pd and Pb, which stops at the alkene. You obtain a cis
A Lindlar catalyst is a catalyst that consists of palladium deposited on calcium carbonate treated with various forms of lead.
Hydrogenation
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Addition of HalogensCl2 and Br2 add to alkynes to form vinyl
dihalides.Product is mixture of cis and trans
isomers.Difficult to stop the reaction at dihalide.